A dc series motor driving an electric train faces a constant power load. It is running at rated speed and rated voltage. If the speed has to be brought down to 0.25 p.u. the supply voltage has to be approximately brought down to

A 200 V, 2000 rpm, 10A, separately excited d.c. motor has an armature resistance of 2 $$\Omega$$. Rated d.c. voltage is applied to both the armature and field winding of the motor. If the armature drawn 5A from the source, the torque developed by the motor is

An electric motor with 'constant output power' will have a torque speed characteristic in the form of a

A 240 V dc series motor takes 40A when giving its rated output at 1500 rpm. Its resistance is 0.3 ohms. The value of resistance which must be added to obtain rated torque at 1000 rpm is: